Bone Broth Math Problem

Iím trying to determine roughly how many calories will be in a given batch of bone broth. I realize that barring investing in a calorimeter, this will just be a hopefully decent guesstimate.

Letís say that 14 gms (1/2 oz) of the average fat has about 100 calories.

If I weigh the bones before and after making the broth, should the difference in weight be the reference for the calories?

For example, I weigh the bones pre-broth. I make the broth; no veggies, just bones, water, a little salt, and a tablespoon of vinegar (negligible calories). The result is (arbitrary numbers here) two quarts of broth. The bones have lost 4 oz of weight in the process.

So, 4 oz of fat would be ~800 calories. Suspended into two quarts of broth, or 8 cups, that would mean that the broth had roughly 100 calories per cup.

Is this remotely logical? Is the assumption that everything the bones lose in weight is fat erroneous?

Thanks in advance for any insights and help.

"Right is right, even if no one is doing it; wrong is wrong, even if everyone is doing it." - St. Augustine

I don't have anything of much use to input, but I track at Sparkpeople and I have two saved in my tracker. Chicken broth at 10 cal. per cup and bone broth at 40cal w/3g fat. I just looked, and there was another one that said 75 cal from homemade chicken broth. I see all kinds of others, just all over the place.

I like the thought process, but there's probably some water weight in the bones that's being lost to the water (and some of that is evaporating throughout your cooking time) which makes the math you're describing uninformative.

Are you going to cool the broth and remove the fat? If so, I wouldn't even worry about the calories in the remaining broth. But then again I don't much worry about calories anyway.

Some of what comes out of the bones are minerals like calcium and such if you use the same bones for several rounds of broth they get crumbly especially if you add ACV to the water. I would just use a guesstimate from established home made broth calorie counts. The first round of broth is much richer from the bones. Later broths are much less.

I don't think the bone weighing would work out, since fat and water are fairly close to the same weight and water will enter the bones to displace any fat that leaves. In other words, the bones may get a bit heavier as the fat leaves.

What I would do for a rough estimate:

1) Stir up the broth really well (suspend all the fat as uniformly as possible)
2) Pour a known amount of broth into a measuring cup.
3) Let sit until fat separates out on surface.

At this point it could go two ways. You could separate out the fat and weigh it (simple/accurate if you have a separator) , or you could convert the fat volume to mass by rule of thumb (food oil in general is about .95 ounces per fluid ounce IIRC, but I have no idea for beef stock fat). So if you have 4 fluid ounces of fat that's ~3.8 ounces weight or ~108 grams or ~972 kcal if I did the math right. If you got 4 ounces of fat from 1 quart of broth, your broth has ABOUT 972 kcal/qt. That's probably as accurate as you will get in a kitchen.